How to join Decking Board at 135°

[okeydokey]

It has been suggested that I get rid of some slightly raised beds (about 6" high) as the wood is rotten and unsightly and replace with 2 octagonal raised beds (about 6 foot across) - so far so good. The interior angles of an Octagon are 135° so the cutting angle of each section is 67.5° on each end, 6" gravel board would do but decking timber is prettier! and is to be the wood for the job.
The sections should marry up nicely and I have found you can buy 135° brackets to go inside the joints to hold them together with 2 on each joint (the ones Ive seen not cheap) and I guess this is the way forward but is there a better way? a nail gun would fix the joints nicely (don't have one) and nails or screws would break out the angled timber at the joints I suspect. Its outside so any glue would not work.
What say you?

 

[PerryGunn]

Biscuits, dowels (or Dominos if you've got the machine) with an external/waterproof glue for vertical alignment plus a flat galvanised (or stainless) plate underneath - if you're going to walk on them, you'll probably want additional supports underneath.

 

[ChaiLatte]

I think arris rail is cut from 3" x 3" timber, so if you screwed a piece of this to a 3" square post, you would have a 135 degree angle to go behind the decking boards. A 4' length of each, cut into eight pieces gives 6" per piece. Slope the top inwards to the centre to shed water and so it does not protrude from the soil.

 

[ChaiLatte]

...plus a flat galvanised (or stainless) plate underneath

I think the boards will be used in a vertical orientation. The joints will be subject to (soil) pressure from the inside, which will tend to separate a biscuited or dowelled joint.

 

[okeydokey]

Yes the boards will be fixed vertical 6" high and perhaps a mechanical fixing would be better than glue.
I think arris rail is cut at 90° but suggesting that fencing wood (thanks) brought me to think of capping rail that goes along the top of close boarded fencing - thats more towards 135 and fixed vertically in the corner joints (they are big enough to take screws) might well do the job plus I have some and its treated wood as well.
And would save buying galvanised brackets - any more cunning plans?

 

[MorrisWoodman12]

Can't you buy flat joining strips and bend them to 135°? Or buy steel strip and make them. You wouldn't need to countersink any holes you drill as the screw heads would, presumably, be hidden. I'd make a jig to clamp to my drill press (assuming you have one) so I don't have to keep marking out the hole positions.
Have fun
Martin

 

[ChaiLatte]

I think arris rail is cut at 90°

Arris rail is a 45 degree right angle triangle. Join it to a square post and the resultant angle is 135 degrees.

While it is true that the two sides that form the 135 degree angle will not be the same length, only the worms will see it.

So long as the worms are not descended from the ones in Pythagorus' time, they will not worry about the irrationality of the square root of 2.

 

[ChaiLatte]

Can't you buy flat joining strips and bend them to 135°?

Screwing from the strip to the decking board limits the screw length to the decking board thickness (maybe 25mm of screw embedment).

Putting a large lump of timber behind the decking board, where it is hidden by the soil, allows a longer fixing to be used from the front (like a standard nearly-invisible-headed outdoor-tolerant decking screw).

 

[MorrisWoodman12]

............ they will not worry about the irrationality of the square root of 2.

Ah! Irrational woodwork is a wonderful thing to behold. But does it look like Escher's drawings?

 

[duke]

It has been suggested that I get rid of some slightly raised beds (about 6" high) as the wood is rotten and unsightly and replace with 2 octagonal raised beds (about 6 foot across) - so far so good. The interior angles of an Octagon are 135° so the cutting angle of each section is 67.5° on each end, 6" gravel board would do but decking timber is prettier! and is to be the wood for the job.
The sections should marry up nicely and I have found you can buy 135° brackets to go inside the joints to hold them together with 2 on each joint (the ones Ive seen not cheap) and I guess this is the way forward but is there a better way? a nail gun would fix the joints nicely (don't have one) and nails or screws would break out the angled timber at the joints I suspect. Its outside so any glue would not work.
What say you?

I find the best way when using nails is to flip the nail over and blunt the point with a hammer. Best to also use an ardox nail , very hard to take apart . This method has been around for hundreds of years. Not my idea!

 

[Phill05]

What about halflap then anchor them with a stainless rod through the joint.

 

[Spectric]

and I have found you can buy 135° brackets to go inside the joints to hold them together

Have you tried

https://tgsupplies.co.uk/product/heavy-duty-galvanised-135-degrees-angle-bracket-corner-brace/

 

[Cabinetman]

What about halflap then anchor them with a stainless rod through the joint.

View attachment 184555

This is a good idea, but suggest 3 or 4 fingers. Also whatever you do will end up the same as the raised beds you are replacing ie rotten, especially relatively thin wood like decking, also nailing it together is a none starter!
I would suggest you build it using plastic decking. Using timber they will only last 3 years - sorry.
Ian

 

[okeydokey]

Thanks Phill05 but my boards will be vertical and similar but different shape to this Homebase product
Good find Spectric but I will need 16 for my two beds which makes it tooo expensive.
I guess I will go along with making/modifying some capping rail (I have some already) from the top of close boarded fencing to make vertical corner braces and screw into each segment joint.
Thanks everyone for your comments - have made me think about the best and inexpensive how to

 

[okeydokey]

I think arris rail is cut from 3" x 3" timber, so if you screwed a piece of this to a 3" square post, you would have a 135 degree angle to go behind the decking boards. A 4' length of each, cut into eight pieces gives 6" per piece. Slope the top inwards to the centre to shed water and so it does not protrude from the soil.

So this afternoon I've taken out the old raised bed timbers and dug it over and levelled the ground a bit ready to start construction of the octagonal frames for the beds.

Next and thanks for the square edge and slope idea
I cut a short piece of arris and matched it to a square section as suggested and yes it works just fine (as I thought it would) but then a cunning plan evolved
Aha I then cut the short arris piece lengthways down the centre rotated one half and the cut edge placed against one of the uncut faces goes to 135° magic
So now Ive just got to cut down the centre of a full arris rail rotate screw sides together cut to length and I have my corner joints/braces of 135°
Next cut the sections at 67.5° join with my braces and off I go.